Hi and thanks for your thorough testing. My explanation is that for certain filesystem / CPU speed combinations, the temp.track() option (turned on on line 7) cleans up the temporary file as soon as it receives the .end() call, and faster than the assert on file existence on line 58 can pass.
Hoping to prevent that, I have attempted a fix (not yet uploaded) that reverts the assert and the .end() function call. So can you please try the 0.8.3-2 version found on salsa https://salsa.debian.org/js-team/node-temp on your autobuilders ? Thanks, Paolo